1. Field of the Invention
The present invention relates to a zoom lens used for optical apparatuses such as digital still cameras, video cameras and interchangeable lenses.
2. Description of the Related Art
High variable magnification zoom lenses whose focal lengths are largely variable are disclosed in Japanese Patent Laid-Open Nos. 2007-003600 and 04-186211. These zoom lenses constituted by at least five lens units including, in order from an object side, a first lens unit having a positive optical power and a second lens unit having a negative optical power. In these zoom lenses, in order to effectively provide a high variable magnification ratio, the first lens unit is largely moved toward an object in an optical axis direction during variation of magnification from a wide-angle end to a telephoto end.
In such zoom lenses, in order to move the first lens unit smoothly, it is necessary to provide a play (hereinafter referred to as an “engagement play”) to an engagement part between a first lens barrel that holds the first lens unit and a supporting lens barrel that supports the first lens barrel movably in the optical axis direction. Therefore, the first lens barrel (first lens unit) is decentered with respect to the supporting lens barrel (second lens unit and other lens units subsequent thereto) in a state where the first lens barrel is moved largely toward the object.
The decentering of the first lens unit at which an axial ray height and an off-axis principal ray height are both large significantly affects optical performance of the zoom lens, in other words, easily causes optical performance deterioration.
The zoom lens disclosed in Japanese Patent Laid-Open No. 2007-003600 is constituted by six lens units including, in order form the object side, positive, negative, positive, negative, positive and negative lens units. The most-object side (positive) lens unit as a first lens unit is largely moved to the object side to perform variation of magnification. In such a zoom lens, since a focusing mechanism can be configured simply, focusing is often performed by moving the first lens unit. Therefore, it is necessary to form a movement mechanism of the first lens unit so as to have a dual structure including a dual engagement play, which causes larger decentering of the first lens unit.
Moreover, the zoom lens disclosed in Japanese Patent Laid-Open No. 04-186211 is constituted by six lens units including, in order form the object side, positive, negative, positive, negative, positive and negative lens units. The most-object side (positive) lens unit as a first lens unit is moved to perform variation of magnification, and the most-image side (negative) lens unit as a sixth lens unit is moved to perform focusing. Therefore, this zoom lens can reduce the engagement play of the first lens unit as compared with the zoom lens disclosed in Japanese Patent Laid-Open No. 2007-003600. However, there is no difference in that an optical performance deterioration sensitivity (ease of deterioration of the optical performance) for the decentering of the first lens unit is high.